The graphic arts and packaging industries utilize a process referred to as ultraviolet curing to avoid problems caused by strict emission control standards and energy costs associated with the drying of inks and other coatings containing volatile solvents. Curing solvent-free inks and other coatings may be achieved by a photopolymerization reaction induced by ultraviolet light, which changes a component of the ink or coating from a liquid to a solid state almost instantaneously. Since these inks and coatings do not contain solvents and are quickly cured, this curing technique is essentially pollution-free and energy efficient.
As will be described further below, to provide for maximum intensity radiation, lamps for ultraviolet curing are typically highly focused units with the coating to be cured being placed precisely in the focal plane containing the highest intensity radiation, which may heat the coating to a high temperature. While this arrangement works well in the curing of coatings with high temperature resistance, many inks and coatings are susceptible to rapid degradation at high temperatures and therefore need to be cured with less intense radiation and cooler temperatures.
Since the energy output of many ultraviolet lamps, particularly those of the electrodeless type, cannot be changed significantly without risk of extinguishing the bulb of the lamp, the intensity of the radiation impinging on the coated substrate of a product is best varied by changing the distance between the lamp outlet and the coated substrate so that the latter is no longer precisely in the focal plane. However, ultraviolet lamp units may be relatively heavy and known means for adjusting the distance between the lamp outlet and the irradiated surface have proven to be cumbersome, time consuming and imprecise.
In addition, many ultraviolet lamp units have an elongated rectangular shape such that the lamp outlet and the radiation beam it produces have a long dimension substantially longer than a short dimension. It may therefore be desirable to rotate the longitudinal axis of the lamp relative to a dimension of the coated substrate to be treated. For example, when treating an elongated strip having a width less than the long dimension of the lamp, it may be desirable to place the longitudinal axis of the lamp at an acute angle relative to the direction of the translational path of the strip to maximize the amount of radiant energy impinging on the strip and thereby minimize the amount of radiant energy bypassing the strip so as to be wasted by heating underlying structure and/or components which may be heat sensitive. In other words, if an elongated strip, a continuous web or other product carrying the coating material to be cured is narrower than the longitudinal spread of the radiation beam provided by the lamp unit, the portions of the beam passing beyond the edges of the product may undesirably impinge upon and heat underlying parts of the housing opposite to the lamp unit outlet. Prior art techniques for rotating the lamp axis relative to the translational path of the product have also proven to be cumbersome, time consuming and imprecise.